In apparatuses called a board, unit or module having mounted thereon a Large Scale Integrated circuit (LSI) or LSI chip, there is generally mounted a JTAG (Join Test Action Group) bus or JTAG interface connected to the LSI device. The JTAG bus is used for testing the LSI device or other purposes. The JTAG bus is a serial bus compliant with International Standard IEEE1149.1, and allows testing of the LSI device during a testing time period other than the apparatus operation time; the testing is performed in response to an access from an external tester or the like which gives boundary scan to the LSI device. The LSI device test may include a processing of specifying an alternating bit of Random Access Memory (RAM) in the LSI device.
Of devices used in the apparatuses, or some LSI device groups such as CPU (Central Processing Unit), some LSI devices are connected to an I2C (Inter-Integrated Circuit) bus or SMbus (System Management Bus). The I2C bus and SMBus are used at the time of controlling the apparatus during the apparatus operation. In this way, like an LSI device connected to JTAG bus and one connected to I2C bus and SMBus, LSI devices connected to buses of different types or standards may be used in a mixed manner in the same apparatus.
I2C bus and SMBus are a general-purpose communication bus used between devices. The I2C bus and SMBus are a two-wire serial bus basically having a clock signal line and data signal line; and a device connected to the serial bus has a unique address. Using this address, the devices communicate with each other via the I2C bus and SMBus.
For example, when LSI devices manufactured by different manufacturers are mounted in the same apparatus, so that the LSI devices are connected to buses of different types, the LSI devices connected to JTAG bus must be controlled via the JTAG bus, and the ones connected to I2C bus and SMBus must be controlled via the I2C bus and SMBus. Accordingly, bus controllers such as a JTAG bus controller and SMBus controller must be mounted correspondingly to the types of buses to which the LSI devices in the apparatus are connected.
FIG. 1 is a block diagram illustrating an example of board in which LSI devices connected to buses of different types are mounted in a mixed manner. The board 1 includes LSI devices 2, 3 and 4, and an SMBus controller 5 and JTAG controller 6. The SMBus controller 5 and LSI devices 2, 3 and 4 are connected to each other via an SMBus 7. The JTAG controller 6 and LSI device 4 are connected via a JTAG bus 8. The SMBus controller 5 is arranged exclusively for the SMBus 7, and can be connected to the outside of the board 1. The JTAG controller 6 is arranged exclusively for the JTAG bus 8, and can be connected to the outside of the board 1.
The method of scanning a circuit such as LSI device has been proposed by Patent Documents such as Japanese Patent Laid-Open No. 9-218248 and Japanese Patent Nos. 2940629 and 3966453.
When the board 1 is controlled via two types of buses, that is, the SMBus 7 and JTAG bus 8, the controllers 5 and 6 each exclusively used for the buses 7 and 8 must be mounted on the board 1, thus raising the cost of the board 1.
Further, when two types of controllers 5 and 6 are arranged to control the board 1, two types of control programs for the board 1 must be prepared, and the control operations by the two types of control programs must be synchronized. Consequently, the control of the whole board 1 becomes complex and difficult to perform.
Thus, an object of one aspect of the present invention is to allow control of a whole apparatus by a simpler control operation while using a less expensive apparatus configuration.